标签：on() hiberna long 常见 div man 方便 stat flush
ManyToOne
多对一，是最常见的表间关系，对应关系数据库中的外键关系。通常用于建立子实体和其父实体的关联关系
@Entity(name = "Person") public static class Person { @Id @GeneratedValue private Long id; //Getters and setters are omitted for brevity } @Entity(name = "Phone") public static class Phone { @Id @GeneratedValue private Long id; @Column(name = "`number`") private String number; @ManyToOne @JoinColumn(name = "person_id", foreignKey = @ForeignKey(name = "PERSON_ID_FK") ) private Person person; //Getters and setters are omitted for brevity }
CREATE TABLE Person ( id BIGINT NOT NULL , PRIMARY KEY ( id ) ) CREATE TABLE Phone ( id BIGINT NOT NULL , number VARCHAR(255) , person_id BIGINT , PRIMARY KEY ( id ) ) ALTER TABLE Phone ADD CONSTRAINT PERSON_ID_FK FOREIGN KEY (person_id) REFERENCES Person
例子：
Person person = new Person(); entityManager.persist( person ); Phone phone = new Phone( "123-456-7890" ); phone.setPerson( person ); entityManager.persist( phone ); entityManager.flush(); phone.setPerson( null ); INSERT INTO Person ( id ) VALUES ( 1 ) INSERT INTO Phone ( number, person_id, id ) VALUES ( ‘123-456-7890‘, 1, 2 ) UPDATE Phone SET number = ‘123-456-7890‘, person_id = NULL WHERE id = 2
OneToMany
一对多用于建立父实体和子实体之间的关系。如果子实体侧没有对应的ManyToOne配置，则这个OneToMany是单向的。如果子实体侧有对应的ManyToOne配置，则这个OneToMany是双向的。双向的关系，可以让开发者在两侧都能获取关联关系。
单向的一对多关系，实例：
@Entity(name = "Person") public static class Person { @Id @GeneratedValue private Long id; @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true) private List<Phone> phones = new ArrayList<>(); //Getters and setters are omitted for brevity } @Entity(name = "Phone") public static class Phone { @Id @GeneratedValue private Long id; @Column(name = "`number`") private String number; //Getters and setters are omitted for brevity } CREATE TABLE Person ( id BIGINT NOT NULL , PRIMARY KEY ( id ) ) CREATE TABLE Person_Phone ( Person_id BIGINT NOT NULL , phones_id BIGINT NOT NULL ) CREATE TABLE Phone ( id BIGINT NOT NULL , number VARCHAR(255) , PRIMARY KEY ( id ) ) ALTER TABLE Person_Phone ADD CONSTRAINT UK_9uhc5itwc9h5gcng944pcaslf UNIQUE (phones_id) ALTER TABLE Person_Phone ADD CONSTRAINT FKr38us2n8g5p9rj0b494sd3391 FOREIGN KEY (phones_id) REFERENCES Phone ALTER TABLE Person_Phone ADD CONSTRAINT FK2ex4e4p7w1cj310kg2woisjl2 FOREIGN KEY (Person_id) REFERENCES Person
Hibernate对单向的一对多关系，两个实体对应两个表，关联关系使用一个中间表来表达。单向一对多在级联操作上比较低效。
双向一对多
Hibernate处理双向一对多关系，按多对一的关系来处理，本质上还是主外键关系。双向的一对多使父子双方都能能力来获取关联关系。使操作更方便，效率等同多对一。
@Entity(name = "Person") public static class Person { @Id @GeneratedValue private Long id; @OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true) private List<Phone> phones = new ArrayList<>(); //Getters and setters are omitted for brevity public void addPhone(Phone phone) { phones.add( phone ); phone.setPerson( this ); } public void removePhone(Phone phone) { phones.remove( phone ); phone.setPerson( null ); } } @Entity(name = "Phone") public static class Phone { @Id @GeneratedValue private Long id; @NaturalId @Column(name = "`number`", unique = true) private String number; @ManyToOne private Person person; //Getters and setters are omitted for brevity @Override public boolean equals(Object o) { if ( this == o ) { return true; } if ( o == null || getClass() != o.getClass() ) { return false; } Phone phone = (Phone) o; return Objects.equals( number, phone.number ); } @Override public int hashCode() { return Objects.hash( number ); } } CREATE TABLE Person ( id BIGINT NOT NULL , PRIMARY KEY ( id ) ) CREATE TABLE Phone ( id BIGINT NOT NULL , number VARCHAR(255) , person_id BIGINT , PRIMARY KEY ( id ) ) ALTER TABLE Phone ADD CONSTRAINT UK_l329ab0g4c1t78onljnxmbnp6 UNIQUE (number) ALTER TABLE Phone ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg FOREIGN KEY (person_id) REFERENCES Person
标签：on() hiberna long 常见 div man 方便 stat flush
原文地址：https://www.cnblogs.com/hengwu/p/9864489.html
